1. Field of the Invention
The present invention relates to a transporting apparatus including a plurality of mutually independent work tables mounting and holding works moving across individual work stations and intermittently moving respective tables depending upon work timing.
2. Related Art
In various automated machine, such as automatic assembly machine, inspection machine of products, mounting machine for mounting chip or the line on a circuit board, and so forth, work or product is transported up to a predetermined work station for performing assembling or inspection operation by robot or the like. In this case, operation is performed in a condition where work or product is stopped in each work station. Transportation of individual work and product has to be performed intermittently so as to repeat moving and stopping in consideration of operation periods in respective work stations.
Therefore, in the prior art, as shown in FIGS. 27 and 28, transporting apparatus 2, 2a employing indexing devices 1 converting constant input rotation into intermittent rotation. In the transporting apparatus 2 shown in FIG. 27, a main sprocket 4 is rigidly secured on an output shaft 3 of the indexing device 1 employing a cam. A chain 5 is wrapped around the main sprocket 4 and a sub sprocket 4a arranged with a given distance to the main sprocket. On the chain 5, a plurality of tables 6 are provided with a predetermined pitch. In this case, the main sprocket 4 and the sub sprocket 4a are rotatable about horizontal shafts. The tables 6 are arranged horizontally between both sprockets 4 and 4a. 
On the other hand, the transporting apparatus 2a of FIG. 28 has similar construction to the foregoing transporting apparatus 2. In this case, not shown main sprocket and sub sprocket are rotated about vertical shafts, and tables 6 are arranged vertically.
Then, in either transporting apparatus 2 and 2a, works 7 are mounted or held on respective tables 6 to carry intermittently. The tables 6 are stopped at positions of not shown work stations arranged on sides of a transporting path of the tables 6 for a predetermined period from time to time. During stopping period, desired operations are performed at respective work stations.
In such conventional transporting apparatus 2 and 2a, in which intermittent indexing is performed, upon moving the tables by output rotation of an indexing device 1, the chain 5 is driven by the sprocket 4 provided on the output shaft 3 of the indexing device 1. For this purpose, positioning accuracy of the table at the work station, in other words, motion accuracy of the table is influenced by a positioning accuracy of the indexing device 1, mounting accuracy of sprocket 4, accuracy of teeth pitch of the sprocket 4, and accuracy of link length of the chain 5. Namely, between the indexing device 1 and the table 6, there are lots of portions requiring high precision, in other words, there are lots of portions causing dimensional errors, to accumulate dimensional errors to degrade motion accuracy or positioning accuracy of the table. On the other hand, wearing can be caused in the portions required accuracy. Cumulative wearing in various portions should results in secular change to increase error to degrade motion accuracy or positioning accuracy of the table even in this viewpoint. Therefore, a transporting length of the transporting apparatus is limited and is difficult to extend,
Furthermore, operation timing in stopping and moving the tables 6, is determined uniformly by intermittent rotation as converted by the indexing device 1 since the tables are fixedly mounted on the chain moving following to output rotation of the indexing device 1. Accordingly, all of tables 6 are driven in uniform timing and uniform motion magnitude with no freedom in determining timing for each individual table.
For the reason set forth above, and despite of the fact that work space of working machines, such as robots or the like provided in respective work stations are variable to be large and small, the work stations have to be arranged with uniform interval adapting to the working machine requiring the largest work space to lower space efficiency. On the other hand, the operation periods in respective work stations are variable to be long and short. Despite of this fact, the stopping period in intermittent transporting operation has to be set adapting to the operation period of the work station requiring the longest operation period to cause waste waiting period in the work station finishing the operation in shorter period. Furthermore, it is difficult to feed large kinds of works 7 or products in the transporting apparatus 2 and 2a. Also, it is difficult to improve operation efficiency.
Even upon transfer of work between former step or next state capable of use of common work table and the linear transporting apparatus, it is not possible to transfer the work together with the work table holding the former to require a separate work transfer device. By providing such separate work transfer device, large installation space can be occupied to lower space efficiency to require substantially high cost.